The present invention relates to a method of and an apparatus for detecting bubbles issuing from a hermetic container, such as a valve or a pump, which is immersed in a liquid, and a method of detecting a leak for determining the presence or absence of a leak in a hermetic container by means of a detected bubble signal.
As a conventional method of detecting a leak, as shown in FIG. 6, for instance, a bubble detecting apparatus 1 has been used in which a bubble collecting section 1a formed in the form of a reverse cone is provided in a lower portion thereof, a pocket section 1b is provided in an upper portion thereof, and a liquid level sensor 1c is provided in this pocket section 1b.
In other words, a hermetic container 2, such as a valve or a pump, is immersed in a liquid, a gas is pumped into the interior of the hermetic container 2, bubbles 3 produced from a leaking portion of the hermetic container 2 are collected in the bubble collecting section 1a, and this state is continued until the bubbles cease to escape from the hermetic container 2. The gas remaining in the pocket section 1b in the upper portion of the bubble detecting apparatus 1 pushes down the liquid level, and the entire volume of the bubbles is measured by detecting the liquid level by means of the liquid level sensor 1c so as to determine the presence or absence of a leak in the hermetic container 2.
With the above-described conventional method of detecting a leak, however, the following problems are encountered since the presence or absence of a leak is determined on the basis of the results of the staying of the bubbles without directly detecting the same.
It is impossible to detect with good accuracy the volume of gas caused by a leak from the hermetic container 2, since both the volume of the bubbles attaching to the periphery of the hermetic container 2 and the volume of the bubbles remaining in recessed portions of the surface of the hermetic container 2 are included in the volume of gas collected by the bubble detecting apparatus 1.
Since the gas collected in the gas detecting apparatus 1 is measured without directly detecting the bubbles, it takes time to determine the presence or absence of a leak. Although this time varies depending on the type of hermetic container, it generally takes three to ten minutes for the adherent bubbles to disappear.
In addition, since the liquid level varies due to the expansion of the gas caused by its temperature, and since a small volume of bubbles causes substantially no change in the liquid level, the accuracy of the measured value has been low and reliability has been lacking.